Sexual minority women (i.e., women who self-identify as lesbian and bisexual) report more heavy drinking, more alcohol-related problems, and higher rates of alcohol use disorders as compared to heterosexual women. Young sexual minority women are particularly vulnerable. Despite this awareness, no studies have examined how relationship factors and partners' alcohol use contribute to hazardous drinking among female sexual minority couples. Minority Stress Theory (MST; Meyer, 2003) contends that experiences of discrimination and stigmatization are associated with negative mental health outcomes and may lead to alcohol use. Grounded in MST, our earlier work [R15AA020424] demonstrated that minority stress is associated with alcohol use and related problems via negative affect among lesbians. Although minority stress and negative affect are key contributors to hazardous alcohol use, sexual minority couples have been systematically excluded from research on relationships and health. Considerable research with heterosexual couples has shown the strong influences that partners' alcohol use and relationship factors have on individuals' alcohol use. Further, a growing body of research has shown that alcohol use is impacted by person-level factors and daily events and emotional states. Extending our previous research, we propose to examine how person-level factors and daily interactions contribute to drinking among female same-sex couples. By employing a daily diary approach it will be possible to examine dynamic daily relationships among alcohol use, relationship experiences, sexual minority stressors, and affect, as well as person-level factors (e.g., baseline characteristics such as legally recognized relationship status, positive sexual identity, and connection to the LGBT community) that may serve as protective factors, and potentially attenuate the association between stressors and hazardous alcohol use. We propose to collect data from both partners in 150 female same-sex couples recruited from an online panel. Participants will individually complete baseline measures of alcohol use, lifetime discrimination, sexual minority identity, relationship status, an connection to the LGBT community followed by 14 days of online daily diary surveys of relationship experiences, stressors, negative affect, and alcohol use. The present research will contribute to our understanding of the mechanisms by which sexual minority women's romantic relationships and experiences of minority stress contribute to alcohol use. In turn, this information can inform efforts to reduce sexual minority women's health disparities and improve their health and well-being. As part of this AREA grant renewal, undergraduate and graduate students will also gain hands on exposure to health science research utilizing a novel methodology to address a serious public health problem.